A power circuit breaker is sold, for example, by Siemens AG under the product name SENTRON 3WL. A safety device of this type serves to protect personnel, systems and equipment. The trip function for interrupting the power flow is generally realized by way of an actuating magnet. This magnetic device can be an electrical coil in which a ferromagnetic rod or plunger is placed. The coil, as a result of being energized, becomes excited and thus generates a magnetic field which drives the plunger out of the coil. Generally, the plunger is held in the coil against a spring force by means of a permanent magnet, with the result that, as a result of the electrical coil being excited, only a short force impulse must be generated in order then to push the plunger out of the magnetic device with the help of the spring.
The functional capability of the power circuit breaker depends, inter alia, on the magnetic device functioning faultlessly. If the power supply lines for the electrical coil are interrupted, if there is a short circuit in the trip circuit or else if there are mechanical problems, such as the plunger being jammed or frozen, the protection device will not work.
In order to monitor the operational capability or to detect possible faults, the magnetic device therefore is subjected to cyclical tests. For this purpose, the power circuit breaker is brought out of the operation mode and into a test mode, in which, however, it cannot then interrupt any current in the event of an electrical fault. In other words, the part of the system which is protected by the power circuit breaker must be switched off or be fed with current by a parallel branch. An on-line test, that is to say during operation of the power circuit breaker, is only known in connection with the electrical parameters of the magnetic device, for instance a continuity test or a measurement of the impedance of the coil. A complete test of the magnetic unit, that is to say including the mechanical functionality, in the course of operation is not possible.